Field of the Invention
The present invention relates to a technique relevant to a display device, and the technique is applied to, for example, a transverse electric field type liquid crystal display,
Description of the Background Art
In recent years, widely used have been new-type display devices having thin planar-shaped display panels utilizing principles such as liquid crystal, electroluminescence (EL), charged corpuscle, and the like, instead of conventional Braun tubes. A liquid crystal display, which is typical of these new-type display devices, has characteristics such as not only thin and light but also allowing low-voltage driving with low power consumption.
In a liquid crystal display, liquid crystal is sealed between two substrates. One of the substrates is an array substrate having a display area in which a plurality of pixels are arranged in matrix and the other substrate is a counter substrate on which a color filter, a black matrix (light shielding film), and the like are formed. The array substrate and the counter substrate are attached to each other with a sealing material.
Among various types of liquid crystal displays, in a thin film transistor (hereinafter, referred to also as “TFT”) liquid crystal display, a TFT serving as a switching element is provided in each pixel on the array substrate. Since each pixel can thereby independently hold a voltage for driving the liquid crystal, it is possible to achieve a high-quality display with less crosstalk.
Further, in each pixel, provided are a gate wire (scanning wire) which controls on/off of the TFT and a source wire (signal wire) for inputting image data, which crosses the gate wire. Usually, an area enclosed by the gate wire and the source wire corresponds to each pixel.
In-plane switching type of a transverse electric field type liquid crystal display performs a display by applying a substantial transverse electric field to a substrate surface. More specifically, a plurality of pixel electrodes and a plurality of counter electrodes (common electrodes) are arranged on the array substrate. In an early-stage in-plane switching type, especially, the pixel electrodes and the counter electrodes are formed in the same layer or different layers in a slit shape or a comb-teeth shape and arranged alternately with gaps in a plan view.
Compared with a conventional TN (Twisted Nematic) type, the in-plane switching type has an advantage of excellent viewing angle characteristics. In the early-stage in-plane switching type where the pixel electrodes and the counter electrodes are arranged alternately with gaps in a plan view, however, electrode portions of the pixel electrodes and the counter electrodes hardly contribute to the display. Therefore, compared with the TN type, the early-stage in-plane switching type has a disadvantage of low light transmittance.
As a transverse electric field type in which this flaw is improved, there is a fringe field switching (hereinafter, referred to also as “FFS”) type. The FFS type is the in-plane switching type in a broad sense and sometimes called the transverse electric field type or the in-plane switching type, not distinguished from the transverse electric field type in which the pixel electrodes and the counter electrodes are arranged alternately with gaps in a plan view.
Also in a FFS liquid crystal display, the pixel electrodes and the counter electrodes are formed on the array substrate (one-side substrate) like in the early-stage in-plane switching type. However, the pixel electrodes and the counter electrodes are arranged vertically in a stacked manner with insulating films interposed therebetween. Further, usually, a lower electrode (either one of the pixel electrode and the counter electrode) has a plate-like (planar) shape and an upper electrode (the other one of the pixel electrode and the counter electrode) has a slit shape having openings or a comb-teeth shape.
In the FFS type, the liquid crystal is driven by a fringe electric field between the upper electrode and the lower electrode. Therefore, the liquid crystal which exists above the electrode portion of the upper electrode (opposite to the lower electrode) is also driven to contribute to the display. The FFS type thereby has an advantage of increased light transmittance, as compared with the IPS type other than the FFS type.
On the other hand, in the transverse electric field type such as the in-plane switching type or the FFS type, a surface of the counter substrate on the side of the liquid crystal is constituted of insulating films such as a black matrix, an overcoat, a color filter, and the like formed of organic resins. In other words, there is no transparent conductive film serving as the counter electrode (common electrode), unlike in the TN type. For this reason, in the transverse electric field type, an electric field generated from a gate-wire leading line on the array substrate produces some effect on the counter substrate.
Specifically, the above-described effect, for example, invites a problem that the counter substrate causes potential variation and this causes display unevenness around a display area in the vicinity of the gate-wire leading line.
Then, as a countermeasure thereagainst, Japanese Patent Publication No. 4011557 proposes that a shield electrode (conductive film) should be arranged on the gate-wire leading line on the array substrate with an insulating film interposed therebetween and then this shields the above-described electric field, to thereby solve the display unevenness.
Japanese Patent Application Laid Open Gazette No. 2000-81638 is also a prior art document relevant to the present invention. Japanese Patent Application Laid Open Gazette No. 2000-81638 discloses a technique in which wires arranged on different layers are connected to each other with a wire arranged on a still upper layer.
The liquid crystal display, generally, is provided with a collectively-driving lighting testing circuit used for inspection therefor or a protection circuit which is popularly called a short ring in some cases. It is not desirable that the above-described countermeasure with the structure disclosed in Japanese Patent Publication No. 4011557 is performed at a portion connecting a wiring layer used for these circuits and the gate wire, since a so-called frame area other than a display portion in which the pixels are collectively formed is widened.
More specifically, in the structure shown Japanese Patent Publication No. 4011557, a transparent electrode covers the gate wire from the upper side with a protection film interposed therebetween but a gate terminal provided in the same layer as the transparent electrode is connected to the gate wire through a contact hole. Therefore, in order to electrically insulate the gate terminal (connected to the gate wire) and the transparent electrode from each other, these elements occupy another area also in a plan view. The extension of such an occupied area invites extension of the above-described frame area and this further prevents improvement in high definition.
Conversely, if the above-described countermeasure cannot be performed, the above-described portion has high density and the area thereof is widened. Around the display area in the vicinity of the portion, there arises display unevenness. This display unevenness becomes remarkable in a display device having high definition.